A power system is constructed by connecting a power generation facility and a load facility through a power transmission facility. There are power systems of various scales, ranging from large-scale systems that connect a plurality of large-scale power plants with a large number of plants, commercial establishments and households to small-scale systems constructed in specific facilities. The power systems of all the scales include an energy management system (EMS) that manages electric power supply/demand in the entire power system. The EMS balances electric power supply from the power generation facilities and electric power demand from the load facilities.
A storage battery system is connected to the power system as described above to be used as one means for balancing electric power supply/demand. Although a large amount of electric power was once thought hard to store, mass storage batteries like lithium ion batteries and sodium sulfur batteries, which are now in practical use, make it possible to store a large amount of electric power. By connecting the storage battery system including such storage batteries to the electric power system, it becomes possible to adopt such an operation as to charge the storage batteries with electric power excessively generated when electric power supply exceeds electric power demand and to discharge electric power from the storage batteries to compensate shortage of electric power caused when electric power demand exceeds electric power supply.
One adequate application example of such a storage battery system is a combination of the storage battery system with a power generation facility using energy of nature, such as sunlight and wind force. The power generation facilities using the energy of nature are widely being introduced in response to increased interest in energy issues or environmental issues of these days. However, the power generation facilities using the energy of nature have a disadvantage that natural factors, such as seasons and weather, tend to affect electric power to be generated and hinder stable supply of electric power. The storage battery system can make up for the disadvantage, so that stable electric power supply can be achieved by combining the storage battery system with the power generation facilities using the energy of nature.
When the storage battery system is connected to the power system, the operation of the storage battery system is managed by the above-mentioned EMS. The storage battery system includes a power conditioning system (PCS) connected to the storage battery. The PCS has a function of converting AC power of the power system into DC power and charging the storage battery with the DC power, and a function of converting DC power of the storage battery into AC power and discharging the AC power to the power system. When a charge/discharge request is supplied from the EMS to the PCS, the PCS operates in response to the charge/discharge request. As a result, charge of the storage battery with electric power from the power system or discharge of electric power from the storage battery to the power system is achieved.
The applicant of the present invention recognizes the following literature as related art of the present invention. FIG. 9 in Patent Literature 1 illustrates one example of a storage battery system connected to the power system.